.\" $OpenBSD: EVP_MD_CTX_ctrl.3,v 1.3 2024/03/05 17:21:40 tb Exp $
.\" full merge up to: OpenSSL man3/EVP_DigestInit.pod
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.\" The original file was written by Richard Levitte <levitte@openssl.org>,
.\" Todd Short <tshort@akamai.com>, Paul Yang <yang.yang@baishancloud.com>,
.\" and Antoine Salon <asalon@vmware.com>.
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.Dd $Mdocdate: March 5 2024 $
.Dt EVP_MD_CTX_CTRL 3
.Os
.Sh NAME
.Nm EVP_MD_CTX_ctrl ,
.Nm EVP_MD_CTX_set_flags ,
.Nm EVP_MD_CTX_clear_flags ,
.Nm EVP_MD_CTX_test_flags ,
.Nm EVP_MD_CTX_pkey_ctx ,
.Nm EVP_MD_CTX_set_pkey_ctx ,
.Nm EVP_MD_CTX_md_data
.Nd configure EVP message digest contexts
.Sh SYNOPSIS
.In openssl/evp.h
.Ft int
.Fo EVP_MD_CTX_ctrl
.Fa "EVP_MD_CTX *ctx"
.Fa "int command"
.Fa "int p1"
.Fa "void* p2"
.Fc
.Ft void
.Fo EVP_MD_CTX_set_flags
.Fa "EVP_MD_CTX *ctx"
.Fa "int flags"
.Fc
.Ft void
.Fo EVP_MD_CTX_clear_flags
.Fa "EVP_MD_CTX *ctx"
.Fa "int flags"
.Fc
.Ft int
.Fo EVP_MD_CTX_test_flags
.Fa "const EVP_MD_CTX *ctx"
.Fa "int flags"
.Fc
.Ft EVP_PKEY_CTX *
.Fo EVP_MD_CTX_pkey_ctx
.Fa "const EVP_MD_CTX *ctx"
.Fc
.Ft void
.Fo EVP_MD_CTX_set_pkey_ctx
.Fa "EVP_MD_CTX *ctx"
.Fa "EVP_PKEY_CTX *pctx"
.Fc
.Ft void *
.Fo EVP_MD_CTX_md_data
.Fa "const EVP_MD_CTX *ctx"
.Fc
.Sh DESCRIPTION
.Fn EVP_MD_CTX_ctrl
performs the digest-specific control
.Fa command
with the command-specific arguments
.Fa p1
and
.Fa p2
on
.Fa ctx ,
which needs to already be set up with
.Xr EVP_DigestInit_ex 3
before calling this function.
Other restrictions may apply depending on the control
.Fa command
and digest implementation.
.Pp
If the
.Fa command
is
.Dv EVP_MD_CTRL_MICALG ,
.Fa p1
is ignored and
.Fa p2
is an output argument of the type
.Fa "char **p2" .
A string specifying the digest Message Integrity Check algorithm
is allocated and a pointer to this string is returned in
.Pf * Fa p2 .
It is the responsibility of the caller to
.Xr free 3
.Pf * Fa p2
when it is no longer needed.
This
.Fa command
is used by
.Xr SMIME_write_ASN1 3
when creating S/MIME multipart/signed messages as specified in RFC 3851.
.Pp
.Fn EVP_MD_CTX_set_flags
sets and
.Fn EVP_MD_CTX_clear_flags
clears all the flag bits in
.Fa ctx
that are set in the
.Fa flags
argument.
.Fn EVP_MD_CTX_test_flags
tests which of the flag bits that are set in the
.Fa flags
argument are also set in
.Fa ctx .
Possible flag bits are:
.Bl -tag -width Ds -offset 2n
.It Dv EVP_MD_CTX_FLAG_NO_INIT
Instruct
.Xr EVP_DigestInit_ex 3
and functions calling it not to initialise the internal data
that is specific to the digest method and its implementation.
.It Dv EVP_MD_CTX_FLAG_ONESHOT
Instruct the digest to optimize for one update only, if possible.
For digest algorithms built into the library, this flag usually
has no effect.
.El
.Pp
.Fn EVP_MD_CTX_pkey_ctx
returns the
.Vt EVP_PKEY_CTX
assigned to
.Fa ctx .
The returned pointer should not be freed by the caller.
.Pp
.Fn EVP_MD_CTX_set_pkey_ctx
assigns
.Fa pctx
to
.Fa ctx .
This is normally used to provide a customized
.Vt EVP_PKEY_CTX
to
.Xr EVP_DigestSignInit 3
or
.Xr EVP_DigestVerifyInit 3 .
The caller retains ownership of the
.Fa pctx
passed to this function and is responsible for freeing it
when it is no longer needed.
.Pp
If the
.Fa ctx
already contains a
.Vt EVP_PKEY_CTX
when this function is called, that old
.Vt EVP_PKEY_CTX
is freed if it was created internally, but if it was also installed with
.Fn EVP_MD_CTX_set_pkey_ctx ,
the pointer to the old
.Vt EVP_PKEY_CTX
is merely replaced by the new pointer and ownership of the old
.Vt EVP_PKEY_CTX
remains with the previous caller.
.Pp
Passing a
.Dv NULL
pointer for the
.Fa pctx
argument is also allowed.
In that case, any
.Vt EVP_PKEY_CTX
already assigned to
.Fa ctx
is dissociated from it as described above, but no new
.Vt EVP_PKEY_CTX
is assigned.
.Pp
.Fn EVP_MD_CTX_md_data
returns the digest method private data of
.Fa ctx .
The space is allocated with a size determined at compile time.
The size is not exposed by an API.
.Sh RETURN VALUES
.Fn EVP_MD_CTX_ctrl
returns 1 for success or 0 for failure.
.Pp
.Fn EVP_MD_CTX_test_flags
returns the bitwise OR of the
.Fa flags
argument and the flags set in
.Fa ctx .
.Pp
.Fn EVP_MD_CTX_pkey_ctx
and
.Fn EVP_MD_CTX_md_data
return pointers to storage owned by
.Fa ctx .
.Sh SEE ALSO
.Xr evp 3 ,
.Xr EVP_DigestInit 3 ,
.Xr EVP_MD_nid 3
.Sh HISTORY
.Fn EVP_MD_CTX_set_flags ,
.Fn EVP_MD_CTX_clear_flags ,
and
.Fn EVP_MD_CTX_test_flags ,
first appeared in OpenSSL 0.9.7 and have been available since
.Ox 3.2 .
.Pp
.Fn EVP_MD_CTX_ctrl
first appeared in OpenSSL 1.1.0 and has been available since
.Ox 5.7 .
.Pp
.Fn EVP_MD_CTX_pkey_ctx
and
.Fn EVP_MD_CTX_md_data
first appeared in OpenSSL 1.1.0 and
.Fn EVP_MD_CTX_set_pkey_ctx
in OpenSSL 1.1.1.
These functions have been available since
.Ox 7.1 .
